java - ROOM持久性库更新和删除不会改变任何东西

Question

我正在编写小型应用程序，并为其使用空间。 SQLite 包装器。 到目前为止，我的代码工作正常，有一些功能无法工作。此外，文档似乎非常不完整，或者在某些方面是错误的。例如dao注解@Update和@Delete。 我慢慢地对使用这个框架感到困惑，并且我考虑重新使用 SQLite API 而不是它。您觉得房间怎么样？

现在是我想问的主要问题。我将向您展示我的代码，也许您会明白为什么不能正常工作。

首先，我的实体和道。它应该代表一个音频文件。

@Entity(tableName = "audiofile")
public class AudioFile
{
    @PrimaryKey(autoGenerate = true)
    private long id;

    @ColumnInfo(name = "title")
    private String title;

    @ColumnInfo(name = "artist")
    private String artist;

    @ColumnInfo(name = "path")
    private String path;

    @ColumnInfo(name = "duration")
    private long duration;

@Dao
public interface AudioFileDao
{
    @Query("SELECT * FROM audiofile WHERE title LIKE :title")
    AudioFile getAudioFile(String title);

    @Query("SELECT * FROM audiofile")
    List<AudioFile> getAll();

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void initAudioFiles(AudioFile... audioFiles);

    @Update
    void updateAudioFile(AudioFile... audioFiles);

//        @Query("DELETE FROM audiofile WHERE id = :audioFileId")
    @Delete
    void deleteAudioFile(AudioFile audioFile);

    @Insert
    void insertAll(AudioFile... audioFiles);

    @Insert
    long insertAudioFile(AudioFile audioFile);
}

这是常规的数据库管理器。

@Database(entities = {AudioFile.class}, version = 1)
public abstract class DbManager extends RoomDatabase
{

    private static DbManager INSTANCE;

    public abstract AudioFile.AudioFileDao audioFileDao();

    public static DbManager getDbManager(Context ctx){
        if (INSTANCE == null){
            INSTANCE = Room.databaseBuilder(ctx.getApplicationContext(), DbManager.class, "playlist").build();
        }
        return INSTANCE;
    }

    public static void destroyInstance(){
        INSTANCE = null;
    }
}

Aaa这是我的测试，它产生了我所有的担忧:

@RunWith(JUnit4.class)
public class DbManagerAndroidTest
{
    private AudioFile.AudioFileDao audioFileDao;
    private DbManager db;

    @Before
    public void createDb()
    {
        Context ctx = InstrumentationRegistry.getInstrumentation().getContext();

        db = Room.inMemoryDatabaseBuilder(ctx, DbManager.class).build();
        audioFileDao = db.audioFileDao();
    }

    /**
     * Test CRUD
     */
    @Test
    public void writeAndRead()
    {
        AudioFile audioFile = new AudioFile.Builder("title")
            .withArtist("artist")
            .withDuration(5)
            .withPath("/this/is/path")
            .build();

        audioFileDao.insertAudioFile(audioFile);
        assertTrue(db.audioFileDao().getAll().size() > 0);
        assertEquals("title", db.audioFileDao().getAll().get(0).getTitle());

        audioFile.setArtist("yo-mama");
        //It won´t update
        audioFileDao.updateAudioFile(audioFile);

        assertEquals("yo-mama", audioFileDao.getAudioFile("title").getArtist());
        //It won´t delete
        audioFileDao.deleteAudioFile(audioFile);
        assertEquals(0, audioFileDao.getAll().size());
    }

    @After
    public void tearDown(){
        db.clearAllTables();
        db.close();
    }
}

预先感谢您的帮助。这件事让我生气。

Answer 1

Now the main question that I want to ask. I will show you my code and maybe you will see, why does not work properly.

我认为您的问题是，当您插入音频文件时，未设置 id，因此音频文件对象audioFile 中的 id 为 0。但是，插入时，id 将自动生成，并且不会为 0，而可能是某个时间插入的 AudioFile 对象的数量 + 1。

如果不设置id，然后使用相同的AudioFile对象来更新/删除，将尝试使用0的id来更新删除。 不会有这样的行。

修复，假设 AudioFile 存在 setId 方法，但不处理失败的插入，可以使用:-

audioFile.setId(audioFileDao.insertAudioFile(audioFile));

可以处理未导致异常的失败插入的修复可能是:-

long insertedId = audioFileDao.insertAudioFile(audioFile);
if (insertedId > 0) {
    audioFile.setId(insertedId);
} else {
    //......... handle not inserted
}

示例/演示

以下代码运行时显示上述内容(您的 Entity 和 Dao 已按原样复制):-

    ...... database built
    mAudioFileDao = mAppDB.audioFileDao();

    AudioFile a = new AudioFile();
    a.setTitle("MySong");
    a.setDuration(5);
    a.setArtist("Fred");
    a.setPath("/thepath");

    logAudioFile(a,"Before Insert into DB");
    long currentId = mAudioFileDao.insertAudioFile(a); //<<<<<<<<<< INSERT INTO DB
    logAudioFile(a,"Immediately after Insert. ID returned from insert is " + currentId);
    a.setId(currentId); //<<<<<<<<<< SET the the id of the AudioFile object a
    logAudioFile(a,"After setting the ID to " + currentId);
    mAudioFileDao.updateAudioFile(a);
    List<AudioFile> audioFileList = mAudioFileDao.getAll();
    for (AudioFile af: audioFileList) {
        logAudioFile(af,"Extracted from DB");
    }
    mAudioFileDao.deleteAudioFile(a);
    Log.d("AUDIOFILEINFO","Attempt to delete Audio File undertaken");
    audioFileList = mAudioFileDao.getAll();
    for (AudioFile af: audioFileList) {
        logAudioFile(af,"After deletion");
    }

logAudioFile方法是:-

private void logAudioFile(AudioFile a, String extra) {
    Log.d(
            "AUDIOFILEINFO",
            "Title is " + a.getTitle() +
                    " ID is " + a.getId() +
                    "\n\tExtra Info is " + extra
    );
}

结果(上面的日志):-

2019-10-06 11:03:39.757 D/AUDIOFILEINFO: Title is MySong ID is 0
        Extra Info is Before Insert into DB
2019-10-06 11:03:39.808 D/AUDIOFILEINFO: Title is MySong ID is 0
        Extra Info is Immediately after Insert. ID returned from insert is 1
2019-10-06 11:03:39.808 D/AUDIOFILEINFO: Title is MySong ID is 1
        Extra Info is After setting the ID to 1
2019-10-06 11:03:39.829 D/AUDIOFILEINFO: Title is MySong ID is 1
        Extra Info is Extracted from DB
2019-10-06 11:03:39.831 D/AUDIOFILEINFO: Attempt to delete Audio File undertaken

<小时/>

What do you think about room?

这是征求意见，所以是题外话。